The present invention relates to an apparatus for receiving a character multiplex broadcast in which when a character image is reduced and divisionally displayed on a cathode ray tube (CRT), a superimposing control to decide whether the image displayed on the divided screen is a television image or a character image can be executed every divided screen, and both of the television image and the character image can be simultaneously mixedly displayed on the CRT.
In recent years, a new media of character broadcasting has been put into practical use and has become gradually widespread. Various kinds of additional functions are being examined to increase the use of character broadcasting.
FIG. 1 shows a schematic block diagram of a character multiplex receiving decoder (hereinafter, simply referred to as a decoder). In the diagram, reference numeral 1 denotes a central processing unit (CPU) to process various kinds of data of the decoder. Reference numeral 2 denotes a read only memory (ROM) in which a program to execute the processing procedure in the CPU 1 is stored; 3 indicates a random access memory (RAM) for working of the CPU 1; 4 an extracting section for extracting a character signal from a video signal and supplying the same to the CPU 1; 5 a system control section to generate various kinds of control signals which are necessary to control each block; 6 a display control section for storing the received character signal into a video RAM 7 or for reading out the character signal from the video RAM 7 and outputting the same to a display terminal; and 8 a Kanji (Chinese character) ROM to store a font (pattern) of a character which was encoded and designated in the character signal. The code encoded in accordance with a predetermined code system (for instance, Japanese Industrial Standard (JIS)) is supplied from the CPU 1 and added as an address into the Kanji ROM 8 and a pattern output corresponding to the code is read out of the Kanji ROM 8 and written into the video RAM 7. By reading out the pattern output from the video RAM 7 and outputting it to the CRT, the character is displayed on the CRT screen.
FIG. 2 is a block diagram of a decoding section as a part of the display control section 6 in FIG. 1.
In the diagram, reference numeral 9 denotes a selector to switch and output one of a raster information signal to designate the background color of the whole screen and a character figure information signal when a character figure picture plane is displayed on the CRT. Reference numeral 10 denotes a detecting circuit to detect the presence or absence of the character figure information signal to generate a switching signal which is necessary when the selector 9 performs the switching operation; 11 indicates a detecting circuit to obtain a YM signal which is necessary to execute the superimposing display; and 12 a detecting circuit to similarly obtain a YS signal. Reference numeral 13 denotes a register to output an indication signal to indicate whether a character figure image to be displayed is an image to be superimposed or not on the basis of the control of the CPU 1. Reference numerals 14 and 15 denote AND gates which are opened only when the indication signal to indicate the superimposing display was input from the register 13.
The operation of the display control section of the above-mentioned character multiplex receiving decoder will now be described hereinbelow.
In the character multiplex broadcasting, in general, sixteen colors comprising eight colors each with two gradations can be displayed. Therefore, all of the colors can be designated by 4-bit data and the following table shows the relationship among the 4-bit data and the display colors.
______________________________________ Ri B G R color ______________________________________ 0 0 0 0 0 black 1 0 0 0 1 red 2 0 0 1 0 green 3 0 0 1 1 yellow 4 0 1 0 0 blue 5 0 1 0 1 pink 6 0 1 1 0 light blue 7 0 1 1 1 white 8 1 0 0 0 transparent 9 1 0 0 1 1/2 red 10 1 0 1 0 1/2 green 11 1 1 0 0 1/2 yellow 12 1 1 0 0 1/2 blue 13 1 1 0 1 1/2 pink 14 1 1 1 0 1/2 light blue 15 1 1 1 1 1/2 white ______________________________________
In the above table, the color is set in a manner such that when the color data is "8" or more, that is, when the bit of Ri is set to "1", the luminance of the color which is expressed by the other three bits is reduced into the half. Although the color data "8" denotes black of 1/2, such a color does not actually exist; therefore, the transparent color is set in such a case. In other words, if the information indicative of color data "8" exists in the character figure information signal, the color at such a position is displayed as a raster color. Namely, the character/ figure is displayed as a transparent image. On the other hand, in the superimposing display mode, a television signal is displayed in place of the raster color display. Therefore, in the superimposing display mode, by designating "8" for both of the raster color and character background color (writing "8" into the video RAM), the superimposed display of both of the character and the television signal can be executed. The YS signal is used to realize such an operation control. Further, since 1/2 white (gray color) in the superimposed mode is difficult to see, the YM signal is used to execute an operation control so as to reduce the luminance level of the television image only in the superimposing display mode.
From the character figure information signal, either one of the character figure information signal and the raster information signal is selected by the selector 9 on the basis of a detection output signal of the detecting circuit 10, so that the final R, G, and B signals are derived. On the other hand, in the superimposing display mode, the superimposing display mode is designated to the register 13 by the CPU 1 and the gates 14 and 15 are opened, thereby obtaining the YM and YS signals.
Although not shown, the R, G, B, and Ri signals are converted into analog signals by simple D/A converters and are synthesized with the television signal together with the YM and YS signals.
The operation of the character multiplex receiving decoder constructed as mentioned above will now be briefly explained hereinbelow.
If the figure information in the character signal extracted from the video signal by the character signal extracting section 4 has been subjected to compression or the like by the process of the CPU 1, the expanding process is executed and, thereafter, the expanded figure information is input to the display control section 6. Or, in the case of the encoded character information, the Kanji ROM 8 is accessed in accordance with the code of such character information and the pattern read out of the ROM 8 is input to the display control section 6. The display control section 6 stores the figure information or pattern into the video RAM 7 in accordance with the input. The display control section 6 simultaneously reads out the display data from the video RAM 7 and provides an output of the R, G, and B signals through a decoding section in FIG. 2.
In addition to the ordinary character broadcasting receiving and displaying operations as mentioned above, as an additional function, as shown in FIG. 3B, there is considered what is called a picture-in-picture mode in which the display area of the character picture plane data is reduced and is displayed by synthesizing onto the ordinary television screen. For instance, the screen in which the ordinary character picture plane area comprises 248 dots in the lateral direction and 204 lines in the vertical direction is reduced into the picture plane area comprising 124 dots.times.102 lines whose size is 1/4 of the ordinary screen and the display is executed on the reduced area. If the ordinary television picture plane data is displayed as the main data and the character picture plane data is displayed as a size of 1/4 at the corner of the main television picture plane area, both of them can be simultaneously seen. On the other hand, if character picture plane data which the user wants to see in detail is input, such data can be soon exchanged and displayed in the main picture plane area in place of the main television picture plane data. Further, as shown in FIG. 3C, the character picture plane data of four picture planes can be also simultaneously displayed. In such a case, the amount of information able to be displayed is increased, thus improving the overall usefulness of the system.
In general, in the case of displaying the character picture plane data on the CRT, a display memory is assigned so as to cover the whole display area. Since the character picture plane data in which the display area is reduced uses a part of the display memory, each time the reduced display is executed in a part of the television image, the rewriting operation must be performed so as to generate the YS signal from the display memory in the other area. Unfortunately, the program required to execute the above data processing is complex and development costs are significant.
On the other hand, in the case of simultaneously displaying four reduced picture planes, if the superimposing display mode is designated for either one of them, a similar problem occurs.